1. Field of the Invention
The present invention relates to a broadcast receiving apparatus to which a smart antenna so structured as to change its directivity direction in the predetermined number of directions and to change its gain in the predetermined number of steps is connected and which receives a television broadcast via the connected antenna and outputs a radio frequency (RF) signal.
2. Description of the Related Art
Conventionally, to receive television broadcasts, directional antennas such as a Yagi antenna and the like have been used. Such directional antennas can receive a weak electric wave because of their high directivity, while they have a disadvantage that they can receive an electric wave from only a given direction. These characteristics do not become a problem so often in Japan or the like where transmission towers which transmit television broadcast waves are concentrated in an area. However, in the USA or the like, there are many districts where a plurality of transmission towers are distributed surrounding an urban area, and when a directional antenna was used, some stations were not able to receive broadcast waves even if there was a short distance from the transmission tower.
Accordingly, to solve these problems, the EIA (Electronic Industries Alliance)—909 (Antenna Control Interface) standard which controls an antenna from a receiving apparatus was made to make it possible to change an antenna's directivity. This is the standard to connect an antenna (hereinafter, called a smart antenna) whose directivity can be changed to a receiving apparatus and to control the antenna from the receiving apparatus side via a modular terminal.
For these television broadcast receiving apparatuses to which a smart antenna can be connected, it is necessary to set the direction (hereinafter, called the optimum receiving direction) of a smart antenna where television broadcast signals can be received in the best condition, and various apparatuses and methods have been proposed to set the optimum receiving direction.
For example, disclosed is a television (TV) broadcast receiving apparatus (patent document 1) which outputs receiving direction control signals to indicate all receiving directions to a connected antenna in succession, measures the receiving intensity of a television broad cast signal received after each receiving direction is indicated, and determines whether or not the connected antenna is a smart antenna based on the measured receiving intensity. According to such a TV broadcast receiving apparatus, it is possible to determine whether or not a connected antenna is a smart antenna, and to carry out an appropriate receiving control according to a determination result, that is, a smart antenna or not.    [patent document 1]JP-A-2006-201285
However, in the TV broadcast receiving apparatus described above, when a television broadcast is received via a connected smart antenna and a RF signal is output, the receiving direction of the smart antenna is changed whenever the channel is changed, and therefore, noise could appear in the output RF signal. Besides, when a television broadcast is received via a connected smart antenna and a RF signal is output, if the receiving direction of the smart antenna is not changed to prevent noise from appearing in the output RF signal, there is a problem that the number of ready-to-receive channels decreases.